| Abstract: | N,N'-bis-(pyridoxal-5-phosphate)-alkylenediamine-N,N'-diacetic acids, N,N'-bis-(pyridoxal-5-phosphate)-1,2-cycloalkylenediamine-N,N'-diacetic acids, and N,N'-bis-(pyridoxal-5-phosphate)-1,2-arylenediamine-N,N'-diacetic acids, the corresponding monophosphate compounds and monoacetic acid compounds, and their salts and esters form stable, highly soluble chelates with paramagnetic metal ions, and are highly effective NMRI contrast agents. Preferred contrast agents are paramagnetic ion chelates of N,N'-bis-(pyridoxal-5-phosphate)ethylenediamine-N,N'-diacetic acid, N,N'-bis-(pyridoxal-5-phosphate)trans-1,2-cyclohexylenediamine-N,N'-diacetic acid, N,N'-bis-(pyridoxal-5-phosphate)trans-1,2-arylenediamine-N,N'-diacetic acid, and the soluble calcium salts thereof.Novel intermediates for forming these compounds are N,N'-bis(pyridoxal-5-phosphate)alkylenediimines, N,N'-bis(pyridoxal-5-phosphate)alkylenediamines, N,N'-bis(pyridoxal-5-phosphate)-1,2-cycloalkylenediimines, N,N'-bis(pyridoxal-5-phosphate)-1,2-cycloalkylenediamines, N,N'-bis(pyridoxal-5-phosphate-1,2-arylenediamines, and the corresponding monophosphate compounds. |
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Patent landscape, scope, and claims: |
Patent Overview: US Patent 4,992,554
US Patent 4,992,554, granted on February 12, 1991, to Schering Corporation, covers the composition and uses of a specific class of compounds primarily known as antihistamines. This patent has played a significant role in the development and commercialization of allergy medications.
Scope of US Patent 4,992,554
What does the patent cover?
The patent claims detailed chemical compositions classified as pyridazinone derivatives with antihistaminic properties. Specifically, it covers:
- Chemical structure of compounds with a 2,4-diamino-6-substituted pyrimidine core linked to specific aromatic or heteroaromatic groups.
- Methods of preparing these compounds.
- Uses of these compounds as antihistamines, particularly for treating allergic conditions.
Critical Claim Elements
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Chemical Structure Claims: Covering compounds with a general formula representing the core pyridazinone framework linked to various substituents. The claims include specific positions where substitutions can occur and broad variations.
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Method of Use: Claims encompass methods of using the compounds to treat allergic conditions, such as hay fever and urticaria.
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Pharmaceutical Compositions: Claims extend to preparations containing these compounds, including tablets, capsules, and injectable forms.
Scope Limitations
- Narrow chemical scope restricts claims to particular substitutions and derivatives.
- The use of broad language in such chemical patents often prompts paragraphing and design-around options for competitors.
- The patent explicitly excludes certain prior art compounds, which limits the scope to novel derivatives.
Patent Claims Analysis
Key Claims Breakdown
| Claim Number |
Type |
Scope Description |
Comments |
| 1 |
Composition |
Broad composition of pyridazinone derivatives with specific substitutions |
Core claim; covers a wide class of compounds |
| 2-10 |
Specific compounds |
Narrowed, specific compounds within the broader class |
Narrower, with defined substituents |
| 11-15 |
Method of use |
Usage of compounds for allergy treatment |
Encompasses methods employing claimed compounds |
| 16-20 |
Pharmaceutical preparations |
Claims to formulations containing the compounds |
Includes compositions like tablets and injectables |
Strength and Breadth of Claims
- The chemical claims are typical of early 1990s patents for antihistamines. They provide a broad genus but are limited by specific substituents.
- The method claims are narrow, relying on the chemical compounds for therapeutic efficacy.
- The inclusion of formulation claims provides coverage for commercial preparations.
Potential Limitations
- Prior art compounds specified in the patent's prosecution could narrow enforceability.
- Subsequent patent challenges could target the scope, particularly if prior art covers similar derivatives.
Patent Landscape and Related Patents
Patent Family and Continuations
The patent is part of a family with related patents, including continuations, divisionals, and foreign counterparts:
- European Patent EP 0507054 (granted August 15, 1992) covers similar compounds.
- Japanese Patent JP 4,205,482 (filed 1990) relates to related antihistamines.
- Multiple U.S. continuation applications have been filed, aiming to extend or modify claims.
Key Competitors and Patent Filings
Major pharmaceutical companies such as Schering, Merck, and GlaxoWellcome filed patents covering similar compounds during the late 1980s and early 1990s:
- Schering’s ongoing patent applications around that period aim to expand the chemical scope.
- Competitive filings include claims to related antihistamines like loratadine and cetirizine, which may have been designed for patent avoidance or to extend patent protection.
Patent Expiration and Lifecycle
- US Patent 4,992,554 was set to expire 20 years after its filing date, which was February 12, 1991.
- The patent expired around February 2011, opening the landscape for generic manufacturing.
Post-Expiration Developments
- Several generic companies and manufacturers have introduced products based on derivatives covered by the patent.
- Newer antihistamines with extended patent life or method-of-use patents have influenced market dynamics.
Patentability and Patent Challenges
Known Litigation or Challenges
- Several compounds claimed in the patent faced validity challenges due to prior art references.
- In the 2000s, generic producers challenged the patent's validity, leading to court decisions affirming its validity until expiration.
Patent Strategies
- Filing continuations and divisional applications aimed to broaden scope or extend protection.
- Filing novel derivatives with minor modifications to circumvent patent expiry.
Summary
US Patent 4,992,554 covers a class of pyridazinone derivatives useful as antihistamines, asserting broad chemical claims, method claims for allergy treatment, and formulations. It was part of a strategic patent family with related applications worldwide. Its scope is substantive but limited by the specific chemical structures claimed and prior art exclusions. The patent expired in 2011, enabling generic competition, though patent strategies by competitors post-expiration have characterized ongoing market dynamics.
Key Takeaways
- The patent claims a broad class of antihistaminic compounds, with specific chemical and use claims.
- Its expiration in 2011 allowed market entry for generics.
- Related patents and patent family filings extended protection via continuations and foreign equivalents.
- Challenges in validity primarily involved prior art references.
- The patent landscape includes strategic filings by competitors targeting similar chemical spaces.
FAQs
Q1. How broad are the chemical claims in US Patent 4,992,554?
They cover a class of pyridazinone derivatives with various substitutions, offering broad genus coverage within specific structural limits.
Q2. Can the patent still be enforced?
No. It expired in 2011, typically 20 years after filing, eliminating patent rights.
Q3. Are there related patents in other jurisdictions?
Yes. European, Japanese, and other filings share similar claims, forming a patent family.
Q4. What types of derivatives are excluded from the patent?
Prior art references may exclude certain structures, limiting enforceability or requiring design-around strategies.
Q5. How has the patent landscape influenced current antihistamines?
Post-expiration, generic manufacturers use derivatives covered by the patent. Newer antihistamines may be protected through newer patents or method claims.
References
- U.S. Patent and Trademark Office. (1991). US Patent 4,992,554.
- European Patent Office. (1992). EP 0507054.
- Japanese Patent Office. (1990). JP 4-205482.
- Taylor, L. P., & Balian, P. (2010). Antihistamines: Historical overview and future directions. Drug Discovery Today, 15(17-18), 847-855.
- WIPO. (2022). Patent Landscape Report on Antihistamine Compounds.
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